dispersed organic matter characterization—TSOP research subcommittee results

Pergamon

0146-6380(94)00083-2

Org. Geochem.Vol. 22, No. 1, pp. 11-25, 1995 ElsevierScienceLtd. Printed in Great Britain

Source rock/dispersed organic matter characterization---TSOP Research Subcommittee Results S. C. TEERMAN, 1 B. J. CARDOTT, 2 R. W. HARDING, 3 M. J. LEMOSDE SOUSA, 4 D. R. LOGAN,5 H. J. PINHEIRO,4 M. REINHARDT,6 C. L. THOMPSON-RIZER7 and R. A. WOODS7 *Chevron Petroleum Technology Co., P.O. Box 446, La Habra, CA 90633, U.S.A. 2Oklahoma Geological Survey, I00 E. Boyd St, Norman, OK 73019, U.S.A. 3Simon-Robertson, Gwynedd LL30 ISA, U.K. 4Organic Petrology Unit, Department of Geology, University of Porto, Praca Gomes Teixeira, 4000 Porto, Portugal SPhillips Petroleum Co., 254 Geosciences Bid, Bartlesville, OK, U.S.A. 6International Geological Consultant, Martinstr. 4, 30659 Hannover, Germany 7Conoco Inc., P.O. Box 1267, Ponca City, OK, U.S.A. Abstract--Because sedimentary organic matter consists of a diverse mixture of organic components with different properties, a combination of chemical and petrographic results offers the most complete assessment of source rock properties. The primary purpose of this Society for Organic Petrology (TSOP) subcommittee is to contribute to the standardization of kerogen characterization methods. Specific objectives include: (1) evaluation of the applications of different organic matter (petrographic) classifications and terminology, and (2) integration of petrographic and geochemical results. These objectives were met by completing questionnaires, and petrographic, geochemical and photomicrograph round-robin exercises. Samples that were selected for this study represent different petrographic and geochemical properties, and geologic settings to help identify issues related to the utilization of different classifications and techniques. Petrographic analysis of the organic matter was completed using both a prescribed classification and the individual classification normally used by each participant. Total organic carbon (TOC), Rock-Eval pyrolysis and elemental analysis were also completed for each sample. Significant differences exist in the petrographic results from both the prescribed and individual classifications. Although there is general agreement about the oil- vs gas-prone nature of the samples, comparison of results from individual classifications is difficult due to the variety of nomenclature and methods used to describe an organic matter assemblage. Results from the photomicrograph exercise document that different terminology is being used to describe the same component. Although variation in TOC and Rock-Eval data exists, geochemical results define kerogen type and generative potential. Recommendations from this study include: (1) A uniform organic matter classification must be employed, which eliminates complex terminology and is capable of direct correlation with geochemical parameters. (2) A standardized definition and nomenclature must be used for the unstructured (amorphous) organic matter category. Subdivisions of this generalized amorphous category are needed to define its chemical and environmental properties. (3) Standardized techniques including multimode illumination, types of sample preparations and data reporting will help eliminate variability in the type and amount of organic components reported. Key words---organic petrology, organic matter classification, maceral, amorphous, multimode illumination, petrographic and geochemical integration, kerogen, source rock

matter originates from a variety of precursors and processes, it varies in petrographic, physical, and chemical properties. The chemical composition of amorphous material can vary from hydrogen-rich to hydrogen-poor for a given thermal maturity (Tissot and Welte, 1984). Petrographic identification and characterization of unstructured organic matter is important because it is a major component of most hydrocarbon source rocks. However, grouping unstructured organic matter into a single generalized category prevents interpretation of its hydrocarbon generative potential and paleoenvironmental

INTRODUCTION AND BACKGROUND

Effective petrographic identification of individual constituents in sedimentary organic matter can describe source rock properties, provide insight into depositional conditions, and define thermal maturity. Petrographically, dispersed organic matter is generally divided into structured and unstructured components. Structured organic matter includes the liptinite, vitrinite, and inertinite macerals, and zooclasts (faunal remains), which are well understood. Because unstructured or amorphous organic o~ 22/i-m

lI

12

S . C . TEERMAN et al.

properties. Numerous terms have been used to describe "unstructured" organic matter, which contributes to confusion in the characterization of this material. Clearly defined and well accepted terminology is essential for the effective description and characterization of unstructured organic matter. Sedimentary organic matter consists of material insoluble in normal organic solvents (kerogen) and a soluble fraction (bitumen). Chemically, kerogen is classified into types I, II, III and IV (Tissot et al., 1974; Harwood, 1977) based on elemental analysis (atomic H/C and O/C). Rock-Eval pyrolysis, which can be used to infer kerogen types, has become a standard method for the chemical evaluation of source rocks. Because a specific kerogen type often consists of a diverse mixture of chemically distinct organic components that react differently during maturation, a combination of chemical and petrographic results offer the most complete assessment of source rock properties. Therefore, it is important for organic petrographic results to complement and correlate with geochemical data and geological results. Previous studies have documented the application and importance of this integrated approach (Jones and Edison, 1978; Larter, 1985; Thompson and Dembicki, 1986). Organic petrology applied to source rock evaluation has evolved from both coal petrology and palynology. Because of the many approaches and goals of organic petrology, a wide variety of techniques and classifications are used. Powell et al. (1982) indicated that the following factors often contribute to a poor correlation between optical and chemical results: unrepresentative kerogen concentrates, inadequate definition of amorphous kerogen and inadequate quantitative estimation of organic matter components. Effective utilization of organic petrology to characterize dispersed organic matter will require a uniform approach. An organic matter classification and its corresponding applications must have a strong scientific basis and provide: (1) acceptable limits of reproducibility for inter- and intra-laboratory results, (2) timely and cost efficient results, (3) data that can be applied by both organic petrologists and other earth scientists, (4) answers to industrial and academic problems, and (5) support of geochemical techniques by an integrated and comparative approach. At the 1987 annual meeting of The Society for Organic Petrology (TSOP), a research subcommittee was formed to review problems related to the integration of organic petrographic data with geologic and geochemical data. An initial TSOP study "Influence of Kerogen Isolation Methods on Petrographic and Bulk Chemical Composition Of A Woodford Shale Sample" was completed by Senftle (1989). OBJECTIVES

T S O P Research Subcommittee

The overall purpose of this subcommittee is to contribute to the standardization of kerogen

characterization methods. Primary objectives of this subcommittee include: (1) evaluation of the applications of different organic matter (petrographic) classifications and terminology, and (2) integration of petrographic and geochemical results. Secondary objectives include evaluation of: (1) techniques for petrographic analysis (light modes, types of sample preparations, etc.), (2) kerogen isolation procedures and (3) methods of sample preparation. There is an urgent need to meet these objectives to provide a standardized and usable system of organic petrographic results. This TSOP subcommittee will complement International Committee for Coal Petrology (ICCP) objectives for the standardization of kerogen characterization methods. ICCP working groups on related subjects include isolation of organic matter and organic matter classifications. Present T S O P study

Specific objectives for this study include: (1) Circulation of a questionnaire to compile and understand petrographic and geochemical methods of kerogen characterization. (2) Petrographic and geochemical round-robin analysis of four samples to evaluate: (1) application of various organic matter terminology and classifications. (2) different petrographic techniques to characterize dispersed organic matter, and (3) geochemical techniques for evaluating kerogen quality. (3) Round-robin description of photomicrographs of the four samples to directly compare nomenclature and properties used to define specific organic components. Results of this study will contribute to identifying and standardizing methods to characterize dispersed organic matter, and integrate petrographic and geochemical results. Although different methods of kerogen isolation lead to discrepancies in petrographic and geochemical results, standardization of preparation procedures was not a primary objective of this specific study. SAMPLES AND PROCEDURES

This specific study involves eight subcommittee members representing industrial, government and academic groups. Participants are a mix of European and North American organic petrologists and geochemists. All individuals or laboratory groups that were committed to completing the petrographic and geochemical analyses in the given time were invited to participate. Identification of participant results has been kept confidential to ensure objectivity and encourage participation by all laboratories. Four thermally immature samples were selected for the round robin study. The samples contain various mixtures of oil-prone, gas-prone and inert organic

Source rock/dispersed organic matter characterization

13

Table I. Sample name, location, and geologicinformation Sample No. 1 2 3 4* Group Wilcox Mesa Verde Formation Monterey Ohio Shale Tropic Shale Member Cleveland Lithology Shale Shale Shale Coal Age Eocene Miocene Miss./Dev. Cretaceous Location Hallsville,TX Arroyo,CA Lewis Co., KY Kane Co., UT Site Sabine mine Outcropt Outcropt Underground mine *Penn State Coal Sample Bank (PSOC No. 1109). tOutcrop samplescontain only minor weathering, which does not affect study objectives.

matter that represent different depositional conditions, geologic age, and wt% total organic carbon (TOC), These samples have a wide range of petrographic and geochemical properties, which help identify issues and questions related to different classifications, techniques, and sample types. Some of these samples were selected because of their difficult petrographic characteristics. Each participating laboratory was provided with representative splits consisting of 5-10g of unprocessed rock. Sample names, locations and geologic information are listed in Table 1. Each laboratory completed kerogen isolation and sample preparation using their normal procedures. A maceral or visual kerogen analysis was requested using both a prescribed classification and the individual classification normally used by each participant. The prescribed classification includes the following categories: amorphous, structured liptinite, vitrinite, inertinite, and other (solid bitumen, zooclasts, etc.), which is generally similar to proposed categories by the ICCP. Subdivisions of the prescribed categories were encouraged. Each participant completed a maceral analysis using their own petrographic techniques but were asked to provide: (1) descriptions of sample preparation procedures, (2) types of light modes and sample preparations used, and (3) presentation of results using their typical format (maceral percentages or description). Participants were asked to complete wt% TOC and Rock-Eval pyrolysis to geochemically evaluate each sample. However, not all participants had access to geochemical instrumentation. Each laboratory was encouraged to conduct other geochemical analyses if possible. In addition, sample splits were sent to various commercial laboratories for wt% TOC, Rock-Eval pyrolysis (whole rock and kerogen) and elemental analyses (atomic H/C and O/C). Kerogen isolation for these analyses was completed at a single locality to eliminate variables related to processing. Although samples were sent to commercial laboratories, contractor evaluation was not an objective of this study. Photomicrographs illustrating specific organic components from the four samples were distributed to determine: (1) nomenclature used by each participant to describe specific organic component(s), and (2) how a specific component fits into their classification. Photomicrographs represent both whole rock

and isolated kerogen preparations (strew mounts and reflectance preparations). Input was also solicited concerning: (1) other terminology that can describe the component, (2) application of certain sample preparations, preparation techniques or light modes to effectively identify the component, and (3) hydrocarbon potential or environmental significance of an individual component. RESULTS AND DISCUSSION

Questionnaire summary A summary of questionnaire results indicates: (1) The primary objectives of petrographic evaluation of dispersed sedimentary organic matter are to define thermal maturity and kerogen quality/hydrocarbon generative potential. Geologic information is secondary. Geochemists and geologists are the main users of organic petrographic data. (2) Most laboratories use both geochemical and petrographic techniques to evaluate kerogen quality. Geochemical results are often used more extensively, and used to select samples for petrographic analyses. Most laboratories compare or integrate petrographic and geochemical results in some manner. (3) For petrographic analysis, most laboratories use a variety of sample preparations and light modes but with different priorities. Results are often combined, depending on the specific sample. Petrographic results are usually reported to the nearest 1-5% (of the total organic matter assemblage in the sample preparation) and incorporated into a computerized data base. Maceral groups are often subdivided for different applications. Most laboratories formally or informally subdivide "amorphous organic matter" using different petrographic properties.

Maceral analysis The prescribed classification was used to directly compare results of individual participants. Although significant differences exist, most laboratories distinguished amorphous-rich samples from those consisting of a mixture of amorphous and structured components. Results for the maceral analysis using

14

S. C. TEERMAN et al. Table 2. Maceral results lbr T S O P samples--prescribed classification Maceral percent Sample name/No.

Lab. No.

Wilcox F m Sample I

I 2 3 4 7

Monterey Sample 2

Ohio Shale Sample 3

Mesa Verde Sample 4

Amorphous

Structured liptinite

Vitrinite

lnertinite

35 35 75 15 40

5 15 15 0 q0

60 30 10 85 3(1

< I 20 Trace Minor 0

I 2 3 4 7

90 90 92 H)0 95

<5 5 5 Minor 5

~ 2 ~ Minor Trace

I 3 Trace Trace 0

I 2 3 4 7

65 90 77 7(I 80

10 0 10 20 10

15 2 S Minor I0

15 8 5 10 Trace

I 2 3 4 7

65 35 70.8 95 60

5 30 4.8 Minor 15

20 10 10.2 5 25

10 25 14.2 Minor 0

Other

Trace solid bitumen

Trace solid bitumen

Note: Not all participants provided data for prescribed classification.

the prescribed classification are listed in Table 2. Good agreement exists for the Monterey sample, which contains predominantly amorphous organic matter. Results for the other three samples, however, display differences in the relative proportions of the amorphous and structured categories. Unfortunately, not all laboratories reported results for the prescribed classification. Differences in reported amounts of vitrinite and inertinite for individual samples are related to: (1) the exclusive use of transmitted or reflected light, (2) type of sample preparation utilized, and (3) petrographic properties used to distinguish the two macerals. Variation in structured liptinite content for individual samples is related to different definitions used by various laboratories, and the light mode and type of sample preparation used. The absence of a standardized definition for the amorphous category contributes to discrepancies in maceral results. For the Wilcox sample, the gradational nature of the amorphous-structured vitrinite contributes to the variation in the reported amorphous content. For the Mesa Verde sample, poor distinction between alginite and amorphous components, and the bituminite-amorphous terminology contribute to variation in maceral results. Results of individual classifications shown in Table 3 generally identify the oil-prone nature of the Monterey, Ohio Shale and Mesa Verde samples, and the gas-prone Wilcox assemblage. However, close comparison of results from individual classifications is difficult due to the wide variety of nomenclature and categories used to describe an organic matter assemblage. Comparison is also difficult because both numerical and descriptive terms are used to report maceral content. Numerous terms

were used in this exercise to describe unstructured organic matter: amorphous, sapropel, sapropelites, alginite, bituminite, SOM (structureless organic matter and sedimentary organic matter), liptinite, amorphogen, organo-mineral matrices, and herbaceous. Individual classifications are shown in Appendix 1. Although each laboratory may be internally consistent and capable of interpreting their results, the large intra-laboratory variation makes interpretation of individual results difficult. Much of this variability is related to the method and classification used to define maceral composition. For the prescribed and individual classifications, inconsistent results are related to: (1) absence of uniform guidelines in classifying organic matter, (2) variation in terminology used to describe organic components, especially amorphous material and (3) different light modes and types of sample preparations used to petrographically evaluate the organic matter. A uniform classification and terminology will contribute to eliminating discrepancies in identifying the type of structured organic components and evaluation of amorphous material. Numerical determination of the relative abundance of organic matter components would contribute to effective comparison of laboratory results. Multimode illumination using different types of sample preparations improves the ability to consistently distinguish and classify individual organic components. Different sample preparations and microscopic techniques have advantages and disadvantages, which are often sample dependent. Many of these techniques are complementary to each other and should be integrated when evaluating and classifying dispersed organic matter.

Source rock/dispersed organic matter characterization

15

Table 3. Maeeral composition/visual kerogen results based on individual classifications a Sample 1 Lab 1 2 3 4 5 6 7 Sample 2 Lab I 2 3 4 5 6 7 Sample 3 Lab 1 2 3 4 5 6 7

b

c

d

e

f

g

h

i

j

35

k

I

m

15

35

n

o

p

q

5

75

15 Z

Z

Z

40

30

<5 5

92

5 X X

Z

5

10

Sample 4 Lab 1 2 3 4 5 6 7

10 100 Y X

X

X

78

X

70.8

35

4.8

95 X 30

30

X Z

Z 10

1 3 Z Z

Z 1

Z 10

15 8 5 Z Z Z 1

20 10 10.2 5

10 25 14.2 Z

Z

5 30

X 20

X 10

65

w

<1 20 Z Z

15 2 8 Z

90 77

v

X

94

65

u

5 2 3 Z

90

100 X

t

X

Z

90

s

60 30 10 85

15 Y

r

Z

Y 15

Z 15

Z

I

Z 10

a, amorphous, unspecified; b, amorphous group 1; c, amorphous group 2; d, amorphous group 3; e, amorphous A; f, amorphous B; g, amorphous C; h, amorphous D; i, sapropel; j, bituminite; k, structured liptinite; I, exinite; m, alginite; n, resinite; o, sporinite; p, SOM; q, herbaceous; r, vitrinite/huminite; s, telocollinite; t, desmocollinite; u, woody; v, inertinite; w, bitumen/exsudate; x, abundant/frequent; y, common; z, rare/minor/present/trace.

Photomicrographs Results from the photomicrograph exercise indicate that different terminology is being used to describe the same component. Although differences in terminology can sometimes be understood, it often leads to discrepancies and confusion. Issues that became evident from this exercise include: (1) The distinction between vitrinite and inertinite is subjective when using only transmitted light. The opaque nature of these macerals can be related to composition and/or particle thickness. (2) It is difficult to consistently distinguish between amorphous and structured vitrinite in samples containing "degraded" vitrinite (Wilcox Fm) or "dense consolidated" amorphous material (Ohio Shale). (3) Multimode illumination (transmitted, reflected and fluorescence) and utilization of a variety of sample preparations are important to identify and classify organic matter. (4) There needs to be a better correlation and standardization of terms when different light modes and sample preparations are used. (5) A consistent application of nomenclature needs to be established to describe fluorescent particles that do not display distinct morphology.

(6) Elimination or replacement of the term herbaceous should be considered, or a clear definition of the term and its correlation to other terminology needs to be established. (7) Organic petrologists are not always comfortable working with both isolated kerogen and whole rock sample preparations. (8) A better correlation needs to be developed between the identification and characterization of unstructured organic matter in isolated kerogen preparations and whole rock. (9) There is difficulty in identifying and classifying unstructured organic matter in reflected light preparations of isolated organic matter. Representative photomicrographs of the round robin analysis, which illustrate specific organic components and corresponding issues, are shown in Plate 1.

Nomenclature--unstructured organic matter A clearly defined and well accepted term is essential for the effective application of organic petrology in characterizing unstructured organic matter. Although a large number of terms exist, many authors from both petrographic and geochemical backgrounds use the amorphous term in classifications and descriptions of sedimentary organic

16

S.C. TEERMANel al.

matter (Combaz, 1964, 1974, 1975, 1980; Burgess, 1974; Raynaud and Robert, 1976; Batten, 1977; Fisher, 1977; Hunt, 1979; D u r a n d and Nicaise, 1980; Alpern, 1980; Robert, 1981; Gutjahr, 1983; Tissot and Welte, 1984; Suzuki, 1984; Mukhopadhyay et al., 1985; Thompson and Dembicki, 1986; Teichmuller, 1986; Senftle et al., 1987). The term amorphinite was defined by van Gijzel (1982) and has been proposed by the ICCP to describe the group of material which exhibits no discrete form or shape. Other terms used to describe amorphous organic matter sometimes erroneously imply that the material has an algal origin and is always oil-prone. Although confusion exists, alginite has been defined by the ICCP (1976) as a structured component consisting of specific recognizable algal remains (Botryococcus, Tasmanites, Gloeocapsarnorpha prisca, etc.). Therefore, alginite is separated from amorphous material, which lacks distinctive morphology and originates from various precursors. Many other terms describing amorphous material subjectively interpret its origin and are confusing to non-experts. Another term used to describe unstructured organic matter is bituminite. Bituminite, originally described by Teichmuller (1974) in coals, was accepted as a component of primary sedimentary organic matter by the ICCP in 1988. It exhibits no specific form but often occurs as a fine-grained groundmass, irregular laminae or pod-like masses. Teichmuller (1986) states that bituminite represents a bacterial decompositional product of algae and plankton with input of bacterial biomass. Subdivisions of bituminite have been described by Teichmuller and Ottenjann (1977) and Creaney (1980), which suggest a variety of precursors, preser-

vational conditions and chemical properties similar to amorphous organic matter. There is an important need to standardize terminology for unstructured organic matter, including the bituminite-amorphous terms. In mature and post-mature source rocks, bitumen (a secondary material) can be an important component that can have an amorphous appearance (Jacob, 1989; Alpern et al., 1992, 1993). This material, which has a wide range of petrographic and geochemical properties, needs to be distinguished from structured and amorphous components. The classification and interpretation of this component can have important implications to source rock studies. Geochemical analyses

Rock-Eval pyrolysis and wt% TOC were completed by six participants and three commercial laboratories. The Monterey, Ohio Shale, and Mesa Verde Coal appear to consist of a Type II kerogen; the Wilcox is a Type III kerogen. Rock-Eval Hydrogen Index and Oxygen Index (HI-OI) results for the four samples are displayed on a modified van Krevelen diagram in Fig. 1. Differences in the $2/$3 are helpful in separating oil-prone assemblages ( > 5 ) from the gas-prone Wilcox sample. Rock-Eval $2 values help define generative potential of these samples. HI results from individual laboratories generally show good agreement for characterizing these four samples. Although variation in H I - O I values > 100mg HC/g OC and 50mg CO2/g OC exist respectively for a single sample, results define kerogen quality and their oil- vs gas-prone nature. W t % TOC

(Plate I on Jacing page) Plate. 1. Photomicrographs of TSOP samples. Round robin participants were asked to describe and discuss properties, classification and nomenclature used for the organic components labeled in each photomicrograph. 1A & B. Wilcox Formation. (A) Transmitted white light, isolated organic matter. (B) Epi-fluorescence, same field of view as (A). l, Does particle represent structured vitrinite or amorphous material? How is the boundary between structured vitrinite and amorphous organic matter defined? 2, Describe classification or subdivision of amorphous material based on petrographic properties. 3, Name of fluorescent component that lacks specific morphology. 2A & B. Ohio Shale. (A) Transmitted white light, isolated organic matter. (B) Epi-illumination,white light; reflectance preparation of isolated organic matter. 2(A) and (B) represent separate fields of view. 1, Name or classification of particle. 2, Classification of amorphous material [same material as in 2(B) # 4]. 3, Does particle represent an amorphous or vitrinitic component? 4, Classification of organic component (bituminite vs amorphous terminology). Compare with component #2 in transmitted light. 5. Classification or name of particle. 3A & B. Monterey Formation. (A) Transmitted white light of isolated organic matter. (B) Same field of view as (A) in epi-fluorescence. 1, Based on petrographic properties, how would this amorphous material be classified? How does this material differ from the Wilcox amorphous organic matter in I(A) and (B) (similar level of thermal maturity). 2, Name or classification of fluorescent particle. How important are these particles in the petrographic characterization of the organic assemblage. 3, Name or classification of particle. What do the opaque particles represent? 4A & B. Mesa Verde Coal. (A) Epi-illumination reflected white light; whole rock preparation. (B) Epi-fluorescence; same field of view as (A). Describe the dominant type of organic constituent in the sample. 1, Name and classification of fluorescent component. For each photomicrograph, describe how additional sample preparations and light modes would assist in the classification of the organic assemblage: 1, application of reflected white light (1 and 3), 2, use of whole rock preparations (1, 2, 3), 3, application of fluorescence (2), 4, use of transmitted light to evaluate isolated organic matter (4).

Source rock/dispersed organic matter characterization

17

I

1A&B Wilcox Fm.

25p.m

2A&B Ohio Shale

3A&B Monterey Fm.

I

4A&B Mesa Verde Coal Plate l--legend opposite

45pro

I

S. (7. TEERMANet

I~

1000

al.

1000

i

-?5,

~ 4

3800

O .~

~ u

5 7 A

_ca 6 0 0

~

B

k; x e) "0

o

C

O

II

-r

c~

~800

O

,1,-

m 600

g

x 0 "O

Lab 2

_c 400

I

HI = 115

Lab 2 HI = 4 4 6

-=400 t0

~ 200

:~ 200

-t"

-r-

/I"-0

x 50

1O0

150

II1

0

200

250

I

0

Oxygen Index (mg COdg Corg) TSOP Sample 1. Wilcox Formation, Texas

~

III

a

250

TSOP Sample 2. Monterey Formation, California

I

1000

J

50 100 150 200 Oxygen Index (mg CO2/g Corg)

1000

Lab

/'

~0 o

~ 81111

e, 7 o A

II em6 0 0

0

n

,r

~

B

g

600

A B

x

"0

Lab 2

"O

¢ 400 --

HI = 476

-~

Lab2 HI = 5 3 7

4OO

C

P

"D "r

-t-

O

0

50 100 150 200 Oxygen Index (mg CO2/g Corg)

250

TSOP Sample 3. Ohio Shale, Kentucky

Fig.

1.

200 -

)) I

0 0

i

"~1' ' ' ~ III

I

50 100 150 200 Oxygen Index (mg CO2/g Corg)

TSOP Sample 4. Mesa Verde Coal, Utah

Rock-Eval Hydrogen and Oxygen Index results from individual laboratories 1"o1"TSOP samples (whole rock). Note Lab. No. 2 did not provide Oxygen Index values.

and Rock-Eval data from each laboratory are listed in Table 4. Consistent patterns appear in H I - O I results for individual laboratories. Differences in HI and OI are related to variation in both TOC, and $2 and $3 values, respectively. Sometimes, differences in TOC and $2 compensate each other resulting in similar HI values. Except for the Wilcox sample, the Ol is not extremely useful in sample characterization. Variation of laboratory results for individual samples are related to sample preparation, instrumentation, and analytical procedures. Rock-Eval HI Ol values of isolated kerogen from three contractor laboratories display good agreement for each sample (Fig. 2 and Table 5). Generally, HI and Ol results are similar for isolated kerogen and corresponding whole rock analyses. However, Ohio Shale and Monterey Formation HI values of isolated

kerogen are approximately 75 and 100 mg HC/g OC higher, respectively. Atomic H/C values display good agreement for individual samples (Fig. 3 and Table 6); however. results are based on analysis from only two contractor laboratories. In contrast to the HI, the atomic H/C more accurately defines the Ohio Shale as a Type II/III kerogen, which agrees with petrographic results. Rock-Eval sometimes has limitations in defining kerogen quality for mixed organic assemblages (Scott, 1992). Minor differences occur in the atomic O/C ratios for relatively oxygen-rich samples. Compared to Rock-Eval Ol values, the atomic O/C effectively defines the nature of these kerogens and their position on maturation pathways. Additional laboratory analysis and a statistical evaluation of the data would be beneficial for the

250

19

Source rock/dispersed organic matter characterization Table 4. Rock-Eval pyrolysis results for TSOP samples (whole rock) Sample Sample 1

Sample 2

Sample 3

Sample 4

Lab.

TOC (wt%)

SI (mg HC/g Rk)

$2 ( m g H C / g Rk)

S3 (mgCO2/g Rk)

PI HI OI (SI/S1 + S2) S2/$3 ( m g H C / g OC) (mgCO2/g OC)

Tin,~ (°C)

I 2 3 4 5 7 A B C

3.45 5.61 6.10 3.84 3.70 3.44 4.31 3.32 3.44

0.25 0.19

3.28 6.46

1.53

0.07 0.02

2.14

95 115

44

423

0.13 0.24 0.16 0.62 0.34 0.41

2.28 3.01 2.96 7.53 3.95 2.81

1.31 2.01 1.94 3.27 1.92 2.66

0.05 0.07 0.05 0.07 0.07 0.12

1.74 1.50 1.53 2.30 2.06 1.06

59 81 86 175 119 82

34 54 56 76 58 77

428 427 423 423 425 417

1 2 3 4 5 7 A B C

4.20 3.76 3.69 3.85 4.20 3.50 5.16 3.91 3.60

0.56 0.40

21.73 16.78

0.69

0.02 0.02

31.49

517 446

16

420

0.31 0.55 0.53 0.60 0.61 0.74

14.77 16.80 14.28 38.31 18.58 19.17

0.97 1.15 1.61 3.48 1.20 1.58

0.02 0.03 0.03 0.01 0.03 0.03

15.23 14.61 8.87 11.01 15.48 12.13

384 400 408 742 475 533

25 27 46 67 31 44

424 418 420 427 420 418

1 2 3 4 5 7 A B C

11.74 13.86 11.90 12.50 11.20 11.96 11.87 12.12 10.90

2.01 2.14

55.04 65.93

1.78

0.03 0.03

30.92

469 476

15

427

142 1.58 2.13 2.24 2.38 2.51

48.38 36.90 40.61 47.27 49.47 50.08

1.33 1.73 4.14 4.62 1.46 1.90

0.02 0.04 0.05 0.04 0.04 0.04

36.38 21.33 9.81 10.23 33.88 26.36

387 329 340 398 408 459

11 15 35 39 12 17

426 427 421 425 420 417

1 2 3 4 5 7 A B C

53.01 57.43

8.01 6.32

301.40 308.10

10.50

0.03 0.02

28.68

569 537

20

435

53.75 54.50 57.38 64.97 48.49 49.29

2.54 10.20 3.79 6.00 5.93 7.14

266.50 236.00 293.10 333.50 242.10 292.90

12.20 15.10 27.10 31.90 12.70 17.80

0.09 0.04 0.01 0.02 0.02 0.02

21.80 15.63 10.83 10.45 19.14 16.44

496 433 511 513 499 594

23 28 47 49 26 36

433 437 428 435 435 436

Note: Labs A - C represent contractor labs.

geochemical study before strict conclusions are stated. Rock-Eval Tmax and vitrinite reflectance data to define thermal maturation of the four samples are listed in Table 4 and Appendix 2, respectively.

provide a quantitative evaluation of the kerogen quality and generative potential. Petrographic analysis identifies individual components that make up the kerogen, which can be used to further interpret and cross check geochemical results. In addition, the hydrocarbon characteristics of individual oil-prone

Comparison of maceral and geochemical analyses Rock-Eval and elemental analysis effectively describe kerogen quality and the hydrocarbon generative potential of these samples. In contrast, it is difficult to use some of the petrographic results to define the generative potential of these organic matter assemblages. Although results of the prescribed classification provide useful information, the lack of definition to the generalized "amorphous" category and variation in intra-laboratory results limit effective characterization. For most individual classifications, inadequate definition of kerogen quality is related to: (1) lack of clear definition for certain petrographic terms, (2) poor correlation between petrographic terms and geochemical data, (3) variation in intralaboratory results, and (4) different methods of reporting results. A combination of geochemical and petrographic results provides the most complete characterization of these samples. Bulk geochemical parameters

10001

~.~

i

I

l / [ i MontmQyFm.

II

IA ® ; 1 0 h ~ l . ~ , I o • [] ~WrdeCod

Ohio Shale

400 200

~Wlloox 0

.0

I

50

Fm. I

-7.~nl

I

100 150 200 Oxygen Index (rag CO~g Cocg)

250

Fig. 2. R o c k - E v a l p y r o l y s i s H y d r o g e n a n d O x y g e n l n d e x results--isolated kerogen from TSOP samples.

S. C. TEERMAN et a/.

20

Table 5. Results of Rock-Eval pyrolysis of isolated kerogens Sample

TOC (wt%)

SI (rag HC/g Rk)*

S2 (mg HC/g Rk)*

$3 (mg CO 2/g Rk)*

HI (mg HC/g OC)

Ol (mg CO 2/g OC)

Tm~x (C)

Sample I Lab A Lab B Lab C

48.34 56.56 56.30

3.53 4.26 5.29

58.55 68.26 63.67

26.02 26.69 33.97

121 122 113

54 47 60

418 416 420

Sample 2 Lab A Lab B Lab C

42.78 57.33 51.89

22.27 29.54 19.60

247.63 299.42 272.80

8.98 8.62 t2.80

579 522 526

21 15 25

422 424 428

Sample 3 Lab A Lab B Lab C

62.50 66.84 66.36

20.63 21.30 13.58

307.58 310.11 315.09

9.54 8.92 9.05

492 464 475

15 13 14

428 426 434

Sample 4 Lab A Lab B Lab C

44.14 48.85 52.10

5+40 8.69 5.10

242.75 239.66 252.65

18.96 16.00 25.71

550 491 485

43 33 49

435 434 438

*Consists of isolated kerogen and small amounts of insoluble minerals. 2.0

[TT

c o n s t i t u e n t s , o r g a n i c m a t t e r o c c u r r e n c e , o r g a n i c prec u r s o r s , a n d d e p o s i t i o n a l c o n d i t i o n s c a n be d e s c r i b e d by petrographic analysis. Organic petrology can effectively identify t h e inertinite c o n t e n t a n d its effects o n g e o c h e m i c a l results, w h i c h is difficult b a s e d o n pyrolysis techniques. Although HI values of the Monterey, Ohio Shale and Mesa Verde samples indicate similar kerogen quality, p e t r o g r a p h i c r e s u l t s d e m o n s t r a t e t h e t y p e a n d a m o u n t o f oil- vs g a s - p r o n e , a n d inert c o m p o n e n t s a r e different. T h e M o n t e r e y c o n s i s t s o f pred o m i n a n t l y o i l - p r o n e c o m p o n e n t s ; t h e O h i o Shale, a m i x t u r e o f several t y p e s o f o i l - p r o n e c o n s t i t u e n t s , a n d g a s - p r o n e a n d inert m a t e r i a l . T h e M e s a V e r d e s a m p l e c o n s i s t s o f a u n i q u e m i x t u r e o f oil- a n d g a s - p r o n e c o m p o n e n t s e m b e d d e d in a n o r g a n i c m a t r i x . F o r t h e Wilcox sample, the HI and atomic H/C document the gas-prone nature of the organic assemblage. Petrog r a p h i c a n a l y s i s identifies t h e g a s - p r o n e vitri-nitic origin o f this a m o r p h o u s m a t e r i a l .

- -

Io

• w ~ l . * .

I +,

,,,m~r~,~,

1.5

-~ 1.0 E <

0.5

0

/

-

Type IV

I

I

I

I

I

0.0S

0.10

0.15 Atomic O/C

0.20

0,9.5

0.30

Fig. 3. Plot of elemental analysis (atomic H/C and O/C) data for isolated kerogens from TSOP samples.

Integration parameters

of

geochemical

and

C o r r e l a t i o n o f a p e t r o g r a p h i c classification to geochemical results provides the integration of the two

Table 6. Results of elemental analyses. Sample

petrographic

% Carbon

% Hydrogen

% Oxygen

% Nitrogen

H/C

O/C

Sample I Lab A Lab B

60.80 61.58

4.14 4.57

19.02 24.00

1.43 1.46

0.82 0.89

0+23 0.29

Sample 2 Lab A Lab B

55.97 58.56

6.10 6.37

7.96 9.42

2.13 2.38

1.31 1.31

0.11 0.12

Sample 3 Lab A Lab B

67.09 69.51

6.15 6.62

7.90 8.54

2.23 2.22

1.10 1.14

0.09 0.09

Sample 4 Lab A 53.31 5.73 13.62 1.22 1.29 Lab B 53.51 5.69 15.58 1.33 1.28 Note: Isolated kerogens were dried under vacuum at 60°C for 24 h prior to analysis.

0.19 0.22

Source rock/dispersed organic matter characterization techniques. Calibration between petrographic and geochemical parameters requires an understanding of the chemistry of different groups of organic components. It has long been recognized that the liptinite, vitrinite and inertinite maceral groups display distinct chemical properties (Seyler, 1943; van Krevelen, 1950; Dormans et al., 1957). More recent work has shown that, within maceral groups, chemical differences occur based on the specific type of vitrinite and liptinite (Gutjahr, 1983). Due to the variation in properties of amorphous material, a single petrographic category prevents accurate characterization of the hydrocarbon generative potential or paleoenvironmental aspects of a source rock. Various studies have demonstrated the geochemical significance of amorphous organic matter subdivisions. Van Gijzel (1982) described three types of amorphous organic matter, which have chemical definition. Sentfle (1984) described fluorescing and non-fluorescing amorphous material, which correlates to chemical properties of an organic matter assemblage. Thompson and Dembicki (1986) demonstrated that the correlation of optically distinct amorphous assemblages to geochemical properties is possible using transmitted, incident white light and fluorescence to recognize petrographic differences. Their work suggests that amorphous nomenclature should describe the optical-chemical properties rather than imply biological origins. Senftle et al. (1987) suggested that multimode illumination permits the distinction of different types of amorphous organic matter. Although different nomenclature is used, Mukhopadhyay (1989) subdivided amorphous materials based on their chemical and petrographic characteristics. An organic matter classification that can be directly correlated to geochemical data will enhance petrographic analysis and complement geochemical results. Jones and Edison (1978) grouped both structured and amorphous organic matter into four categories generally equivalent to the four defined kerogen types (Tissot et al., 1974; Harwood, 1977). This approach, which eliminates complex petrographic terminology, emphasizes the identification of individual petrographic components based on their chemical properties. In addition to morphological information, this approach provides definition to bulk geochemical parameters and an important crosscheck for petrographic results. RECOMMENDATIONS AND FUTURE DIRECTION

There is a need to develop a uniform petrographic classification that facilitates effective organic matter characterization and provides additional value to source rock evaluation. A standardized, well defined classification is needed that routinely uses well understood nomenclature. Acceptable limits of reproducibility need to be established to provide consistent results. Organic petrographic results must compOG 2 2 / 1 ~

21

lement and provide additional information to established geochemical parameters and geological information. Unless these attributes of a uniform classification are achieved, future advancement and utilization of organic petrology will be difficult. The following recommendations result from this study: (1) A uniform organic matter classification must be employed, which eliminates complex terminology and is capable of direct correlation with geochemical parameters. (2) A standardized definition, nomenclature, and application of amorphous organic matter is needed that can help provide useful and reproducible results. (3) Subdivisions of the amorphous category are needed to better characterize its chemical (hydrocarbon generative potential) and environmental properties. (4) Standardized techniques including utilization of multimode illumination and different sample preparations will help eliminate some of the variability in the amount and type of structured and amorphous components identified. Future direction of this subcommittee includes: (1) additional photomicrographs of round robin and other samples, (2) standardization of microscopic techniques, (3) address "amorphous problem" and nomenclature, (4) define consistent subdivisions of amorphous organic matter, and (5) integration of microscopic and geochemical results. Future work should be carried out with the ICCP and other groups. Acknowledgements~Gratitude is expressed to all subcommittee participants and corresponding laboratories for their contributions. Chevron Petroleum Technology Company provided financial support to help complete this study. The TSOP Research Committee provided financial support for publication of color photomicrographs. D. Logan (Phillips) provided some of the round robin samples. Constructive comments from reviews by D. K. Baskin, J. R. Castafio, W. G. Dow and J. Thompson contributed to the manuscript. T. T. Ta (Chevron) provided technical assistance in carrying out this study. Appreciation is expressed to S. E. Kim (Chevron) for graphical support in completing this manuscript.

REFERENCES

Alpern B. (1980) Petrography of kerogen. In Kerogen. Insoluble Organic Matter from Sedimentary Rocks (Edited by Durand B.), pp. 339-383. Editions Technip, Paris. Alpern B., Lemos de Sousa M. J., Pinheiro H. J. and Zhu X. (1992) Optical morphology of hydrocarbons and oil progenitors in sedimentary rocks--relations with geochemical parameters. Publ. Mus. Labor. miner, geol. Fac. Cienc. Porto N. S. 3, 1-21. Alpern B., Lemos de Sousa M. J., Pinheiro H. J. and Zhu, X. (1993) Detection and evaluation of hydrocarbons in source rocks by fluorescence microscopy. Org. Geochem. 20, 789-795. Batten D. (1977) Proc. I V Int. Paly. Conf., Lucknow, India.

22

S.C. TEERMAN el a/.

Burgess J. D. (1974) Microscopic examination of kerogen (dispersed organic matter) in petroleum exploration. Geol. Soc. Am. Spec. Paper 153, 19-30. Combaz A. (19643 Les palynofacies. Bey. Micropaleo. 7, 205-218. Combaz A. (1974) La matiere algaire et Forigine du petrole. In Advances in Organic Geochemistry 1973 (Edited by Tissot B. and Bienner F.), pp. 423438. Editions Technip, Paris. Combaz A. (19753 Essai de classfication des roches carbonees et des constituants organiques des roches sedimentaires. In Petrographie de la Matiere Organique des Sediments, Relations avec la Paleotemperature et le Potentiel Petrolier (Edited by Alpern B.), pp. 9 3 101. Centre National de la Recherche Scientifique, Paris. Combaz A. (1980) Les kerogenes vus au microscope. In Kerogen. Insoluble Organic Matter .[?om Sedimentary Rocks (Edited by Durand B.), pp. 55 111. Editions Technip, Paris. Creaney S. (19803 The organic petrology of the Upper Cretaceous Boundary Creek Formation, BeaufortMackenzie basin. Bull. Can. Pet. Geol. 28, 112 129. Dormans H. N. M., Huntjens F. J. and van Krevelen D. W. (1957) Chemical structure and properties of coalcomposition of the individual macerals (vitrinites, fusinites, micrinites, and exinites). Fuel 36, 321 339. Durand B. and Nieaise G. (1980) Procedures for kerogen isolation. In Kerogen. Insoluble Organic Matter from Sedimentary' Rocks (Edited by Durand B.), pp. 35 53. Editions Technip, Paris. Fisher M..I. (19773 Proc. 1V Int. Po(v. ConiC, Lucknow, India. van Gijzel P. (1982) Characterization and identification of kerogen and bitumen and determination of thermal maturation by means of qualitative and quantitative microscopical techniques. In How to Assess Maturation and Paleotemperatures. SEPM Short Course No. 7. pp. 159 216. Gutjahr C C. M. (1983) Introduction to incident-light microscopy of oil and gas source rocks. Geol. Mtljnbouw 62, 417-425. Harwood R. J. (19773 Oil and gas generation by laboratory pyrolysis of kerogen. AAPG Bull. 61, 2082 2102. Hunt J. M. (1979) Petroleum Geochemistry and Geology. Freeman, San Francisco. International Committee for Coal Petrology (1963, 1971, I976) International Handbook qf Coal Petrology, 2nd edition (1963), 1st Supplement (1971), 2nd Supplement (1976). Centre National de la Recherche Scientifique, Paris. Jacob H. (1989) Classification, structure, genesis and practical importance of natural solid oil bitumen ("migrabitumen"). Int. J. Coal Geol. 11, 65 79. Jones R. W. and Edison T. A. (1978) Microscopic observations of kerogen related to geochemical parameters with emphasis on thermal maturation. In Low Temperature Metamorphism of Kerogen and Clay Minerals (Edited by Oltz O. F.), pp. 1 12. Society of Econ. Paleont. Min. van Krevelen D. W. (1950) Graphical-statistical method for the study of structure and reaction processes of coal. Fuel 24, 269 284. Larter S. R. (19853 Integrated kerogen typing in the recognition and quantitative assessment of petroleum source

rocks. In Petroleum Geochemistry in Exploration of the Norwegian Shell" (Edited by Thomas B. M. et al.), pp. 269-286. Graham & Trotman, London. Mukhopadhyay P. K. ([989) Characterization of amorphous and other organic matter types by microscopy and pyrolysis-gas chromatography. O r g . Geochem. 14, 269 284. Mukhopadhyay P. K., Hagemann H. W. and Gormly J. R. (19853 Characterization of kerogens as seen under the aspect of maturation and hydrocarbon generation. Erdol Kohle Erdgas Petrochem. 38, 7 18. Powell T. G., Creaney S. and Snowdon L. R. (19823 Limitations of use of organic petrographic techniques for identification of petroleum source rocks. AAPG Bull. 66, 430 435. Raynaud J. F. and Robert P. (t976) Les methodes d'etude optique de la matiere organique. Bull. Centr. Rech. Pau-SNPA If[, 109 127. Robert P. ( 198 I) Classification of organic matter by means of fluorescence; applications to hydrocarbon source rocks. Int. J. Coal Geol. I, 101 137. Scott J. (I 992) Accurate recognition of source rock character in the Jurassic of the North West Shelf, Western Australia. APEA 32, 289 299. Senftle J. T. (1984) Optical analysis of kerogen its role in an integrated approach for kerogen typing. North Arnerican Coal Petrographers Meeting Programs and Abs., Merrilville, Ind. Senftte J. T. (1989) Influence of kerogen isolation methods on petrographic and bulk chemical composition of a Woodford Shale sample. TSOP Research Subcommittee Report ( 10/31/89). Senftle J. T., Brown J. I-L and Latter S. R. (19873 Refinement of organic petrographic methods for kerogen characterization. Int. ,L Coal Geol. 7, 105--117. Seyler C. A. (1943) The relevance of optical measurements to the structure and petrology of coal. In Proceedings, Cor![erence on the Ultra:line Structure of Coals and Cokes, London, pp. 270 289. Suzuki N. (1984) Characteristics of amorphous kerogens fractionated from terrigenous sedimentary rocks. Geochim. Cosmochim. Acta 48, 243 249. Teichmuller M. (19743 lrber neue macerale der liptinitgruppe und die entstehung des micrinits. Fortschr. Geol. Rheinld. Wes(f 24, 37 64. Teichmuller M. (19863 Organic petrology of source rocks, history and state of the art. Org. Geochem. 10, 581 599. Teichmuller M. and Ottenjann K. (1977~ Art und diagenese von liptiniten und lipoiden stoffen in einem erdolmuttergestein auf grund fluoreszenzmikroskopiseher untersuchungem. Erdol Kohle Erdgas Petrochem. 30, 387 398. Thompson C. L. and Dembicki H. (19863 Optical characteristics of amorphous kerogens and the hydrocarbongenerating potential of source rocks. Int. J. Coal Geol. 6, 229 249. Tissol B. and Welte D. I t (1984~ Petroleum Formation and Occurrence. Springer, Berlin. Tissol B. P., Durand B., Espitalie J. and Combaz A. (1974) Influence of nature and diagenesis of organic matter in formation ~)f petroleum. AAPG Bull. 58, 499 506.

Source rock/dispersed organic matter characterization

APPENDIX Amorphous

Herbaceous

Woody

23

1

Vitrinite

InerUnite

Solid Bitumen

1olo Amorphous*

Structured Liptinite

(I)

(ll)

Vitdnite (III)

Inertinite

Solid Bitumen

(iv)

Group1 I Group2 I Group3 I I

*Amorphous Groups 1-3 Generally Equivalent to Type I-III Kerogen

Liquid Exinlte Prone

Alglnite

Type II Terrestrially Dedved

Structured But Occasionally Amorphous

LipUnite

Herbaceous

Phyrogen

Phytoclast (Fluorescent)

Type I Lacustrine Algae

Amorphous Kerogen

Sapropel or Liptinite

Amorphous

Amorphogen

ProUstoclast

Type III

Structured Kerogen (Rarely (?) Amorphous)

Huminite

Woody

Hylogen

Phytoclast

Type IV

Structured Kerogen

InertJnite

Coaly

Malanogen

Inertinite

Type II Madne Algae Gas Vltrlnlto Prone

arbor (InerUnite)

Kerogen Composition Data % (Visual, From Microscopy) InerUnite

Vitrinite

Sapropel

% (Calculated) Inertinite

Vitrinite

Alginite Sapropel

Wxy Sapropel

--continued overleaf

24

S.C. TEERMANet al.

Rock: OM:

[ ] Coal Pyrite: [ ] [] [] []

OM Pyrite Quantity Oxidation MaceralComposition

[] [] [] [] [] [] [] [] [] [] [] [] [] [] [] [] [] []

Vitrinite

Inertinite ~

X = Frequent V = Abundant

Liptinite

+ = Common

/ = Little

Macemls ReflectedLight Inertinite Huminite/ Vitrinite Polymacente Bitumenite Sporinite Cutinite Resinite Liptodetrinite Telalginite Lamalginite Migrabitumen Exsudates Organo-MineralMatrices Zooclasts Proportion: Fluo/Non-FluoOM: Pollution: Oxidationor Irradiation: Conclusions:

Framboidal Crystaline Massive Glauconite SOM Telocollinite Telinite Desmocollinite Sporinite Cutinite Resinite Liptodetrinite Alginite Microplankton Sclerotinite Fusinite Semitusinite Macrinite Micdnite Bituminite DeadCarbon Graphite

- = Rare

Fluorescence

Reworking:

Source rock/dispersed organic matter characterization Descriptive Sheet of Whole Rock Raw Sample (as received): Nature: Mass (g): Color: Black Coaly Particles Migrabitumen Clasts (Reservoirs) Peri: Central: Impregnated Gloval: None: Shales Matrix Fluo Color Liptinite Fluo Color Q: 650/500 HC Neoproduction Drops: Films + Networks: Fading Reaction Under UV: HC Dissolution In-Resin Relative Fluo Intensity:

APPENDIX

2

Table A2. Vitrinite Reflectance Data TSOP Samples Sample and Lab No. Sample 1 1 2 3 4 5 6 Sample 2 I 2 3 4 5 6 Sample 3 1

2 3 4 5 6 Sample 4 1 2 3 4 5 6

% Reflectance

n

a

0.40 0.46 0.40 WR 0.31 Conc 0.40 0.41 0.45

55 61 65 60 55 76 I 10

0.03 0.02 0.04 0.06 0.02 0.03 0.05

0.32 0.32 0.27 0.29 0.33 0.30 0.33

26 26 10 31 55 15 70

0.04 0.02 0.05 0.06 0.04 0.02 0.04

0.39

35

0.03

0.44 WR 0.44 Conc 0.46 (0.4-0.45) 0.39

40 23 8

0.06 0.05 0.04

21

,0.05

50 35 100 55 39 100

0.03 0.03 0.04 0.04 0.04 0.04

0.43 0.47 0.38 WR 0.42 0.41 0.36

25